The G protein-coupled receptors (GPCRs) are integral membrane proteins that are involved in cellular signal transduction. GPCRs respond to a variety of extracellular signals, including neurotransmitters, hormones, odorants and light, and are capable of transducing signals so as to initiate a second messenger response within the cell. Many therapeutic drugs target GPCRs because those receptors mediate a wide variety of physiological responses, including inflammation, vasodilation, heart rate, bronchodilation, endocrine secretion and peristalsis.
Diseases such as asthma, chronic obstructive pulmonary disease (COPD), psoriasis, and rheumatoid arthritis (RA) generally are considered to have an inflammatory etiology involving T helper cells, monocyte-macrophages and eosinophils. Current anti-inflammatory therapy with corticosteroids is effective in asthma but is associated with metabolic and endocrine side effects. The same is possibly true for inhaled formulations that can be absorbed through lung or nasal mucosa. Satisfactory oral therapies for RA or COPD currently are lacking.
Molecular cloning of HM74 from human monocytes predicted HM74 to be a chemokine receptor (Nomura et al., Int. Immunol. (1993) 5(10):1239-1249). HM74 is expressed primarily in bone marrow, spleen, tonsil and trachea.
Human cells also contain a related but distinct receptor, HM74A. The amino acid sequences of HM74 and HM74A are about 95% identical. However, the ligand of HM74A is known whereas the ligand of HM74 is unknown. Niacin or nicotinic acid is the HM74A ligand, Wise et al., J. Biol. Chem. 278:9869-9874, 2003. Niacin is but a poor activator of HM74.
The mouse genome contains an HM74A gene but not an HM74 gene.
Under certain circumstances, HM74 and HM74A demonstrate coregulation. Using Taqman-PCR, applicants found that HM74 and HM74A expression is induced 50-fold by TNFα in granulocytes and 10-20-fold by LPS or TNFα in monocytes. HM74 and HM74 expression also are induced 4-5-fold in normal human bronchial epithelial cells with the TH2 cytokines, IL-4 or IL-13, known to be important in the etiology of asthma. HM74 and HM74A expression are upregulated in human primary eosinophils by IL-5. Finally, pulmonary HM74A expression is upregulated in a murine experimental asthma model.
The restricted tissue distribution of HM74 and HM74A, and the regulation thereof suggest a role for HM74 and HM74A in inflammatory processes, such as asthma, COPD and RA.
Given the role GPCRs have in disease and the ability to treat diseases by modulating the activity of GPCRs, identification and characterization of GPCR ligands can provide for the development of new compositions and methods for treating disease states that involve the activity of a GPCR. The instant invention identifies and characterizes molecules that engage HM74, and provides compositions and methods for applying the discovery to the identification and treatment of related diseases.